Ministry of Earth Sciences
All India Weather Inference 
Present heat wave conditions very likely to continue to prevail mainly during next 24 hours days over plains of northwest India, Central India & adjoining interior parts of eastern India
Conditions are favourable for further advance of Southwest Monsoon into some parts of Maldives-Comorin area and adjoining southeast Arabian Sea, remaining parts of Andaman Sea and some more parts of south and central Bay of Bengal during next 48 hours
According to the National Weather Forecasting Centre of the India Meteorological Department:
♦ In view of the enhanced cloud cover and deepening of southwesterly winds upto mid tropospheric levels, Southwest Monsoon has further advanced into some more parts of south Bay of Bengal, most parts of Andaman Sea and Andaman & Nicobar Islands today. The Northern Limit of Monsoon  passes through Lat.5°N/Long.82°E, Lat.7°N/Long.86°E, Lat.10°N/Long.90°E, Port Blair, Lat.15°N/Long.97°E.
♦ Conditions are becoming favourable for further advance of Southwest Monsoon into some parts of Maldives-Comorin area and adjoining southeast Arabian Sea, remaining parts of Andaman Sea and some more parts of south and central Bay of Bengal during next 48 hours.
♦ The cyclonic circulation over southwest Arabian Sea now lies over westcentral and adjoining southwest Arabian Sea extending upto mid tropospheric levels. Under its influence, a low pressure area is very likely to form over the same region around 29th May. It is very likely to concentrate into a Depression over the same region during the subsequent 48 hours.
♦ The Western Disturbance as a cyclonic circulation over Afghanistan & neighbourhood now lies over northeast Afghanistan & neighbourhood at 5.8 km above mean sea level.
♦ The eastwest trough at mean sea level from East Uttar Pradesh to Nagaland across Bihar, SubHimalayan West Bengal and Assam persists and now extends upto 1.5 km above mean sea level.
♦ The cyclonic circulation over Punjab & neighbourhood extending upto 2.1 km above mean sea level persists.
♦ The trough from south Chhattisgarh to interior Tamilnadu now runs from Rayalaseema to interior Tamil Nadu and now extends upto 1.5 km above mean sea level.
♦ The cyclonic circulation over southwest Bay of Bengal & neighbourhood now lies over southwest Bay of Bengal off Sri Lanka coast between 2.1 and 4.5 km above mean sea level.
♦ The cyclonic circulation over Coastal Karnataka & neighbourhood at 2.1 km above mean sea level has become less marked.
♦ The northeastsouthwest trough in westerlies roughly along Longitude 88°E to the north of Latitude 23°N between 1.5 & 2.1 km above mean sea level has become less marked.
HEAT WAVE
Meanwhile, due to prevailing dry northwesterly winds over plains of northwest India, Central India & adjoining interior parts of eastern India, present heat wave conditions very likely to continue to prevail mainly during next 24 hours.
Meteorological sub-division wise,
- Heat wave conditions at many places with severe heat wave in isolated pockets very likely over Vidarbha;
- Heat wave conditions at a few places with severe heat wave in isolated pockets over West Rajasthan;
- Heat wave conditions in some pockets over Haryana, Chandigarh & Delhi, West Uttar Pradesh, Madhya Pradesh and East Rajasthan and in isolated pockets over Punjab, Bihar, Jharkhand, Odisha, Saurashtra & Kutch, Madhya Maharashtra, Marathwada, Telangana and North Interior Karnataka during next 24 hours.
Heat Wave is considered if maximum temperature of a station reaches at least 40°C or more for Plains, 37°C or more for coastal stations and at least 30°C or more for Hilly regions. Following criteria are used to declare heat wave:
a) Based on Departure from Normal
- Heat Wave: Departure from normal is 4.5°C to 6.4°C
- Severe Heat Wave: Departure from normal is >6.4°C
b) Based on Actual Maximum Temperature 
- Heat Wave: When actual maximum temperature ≥ 45°C
- Severe Heat Wave: When actual maximum temperature ≥47°C
To declare heat wave, the above criteria should be met at least in 2 stations in a Meteorological subdivision for at least two consecutive days and it will be declared on the second day.
|
|
HEAT WAVE WARNING 
Green

|
|
Normal Day
|
|
Maximum temperatures are near normal
|
|
Yellow Alert

|
|
Heat Alert
|
|
Heat wave conditions at district level likely to persist for 2 days
|
|
Orange Alert

|
|
Severe Heat Alert for the day
|
|
 Severe heat wave conditions persist for 2 days.
 With varied severity, heat wave is likely to persists for 4 days or more
|
|
Red Alert

|
|
Extreme Heat Alert for the day
|
|
 Severe heat wave persists for more than 2 days.
 Total MAXIMUM TEMPERATURES number of heat/severe heat wave days likely to exceeds 6 days.
For more details kindly visit www.imd.gov.in